Numerous situations exist where water is piped under pressure to a number of final delivery points in which the distribution system is primarily concerned with delivery of a specified volume of water delivered in a given time period. Typical situations for this are agricultural sprinkler irrigation systems, home garden sprinkler systems, and numerous industrial water delivery systems and timed tank filling operations. Due to a number of factors water pressure of different points within the system may vary, for example, an agricultural or estate sprinkler system may be located in a hilly area, in which case sprinklers at the top and bottom of the hill will have different pressures reflecting the altitude difference. Similarly, the system pressure may vary with time rather than location. For example, other uses on the same main water supply vary from time to time, or the degree to which the supply valve is opened may vary causing the system's initial delivery pressure to vary.
Generally, the final volume rate of flow of water in these systems varies directly with the pressure at the delivery point, e.g., within a broad pressure range, an irrigation sprinkler's water delivery per unit time increases linearly with the water pressure. This creates several problems. First, too high a pressure and consequently high volume flow delivery will rapidly increase the wear on the parts of the delivery system, such as rotating sprinkler heads, increasing capital investment costs. Secondly, a delivery of excessive water simply wastes water, an obviously undesirable consequence. Additionally, for many applications, a constant flow response regardless of pressure will allow for delivery of a set water volume to be controlled solely by timing the system, decreasing monitoring difficulties.
It must be appreciated that to be practical, the control device must be inexpensive. If the delivery is to be controlled just before final delivery, e.g., at each sprinkler head in an irrigation system, then large number of restrictors must be used, and cost per unit must be kept low. Also a wide variety of fittings exist in these systems, necessitating a great flexibility for adapting to varied situations for a control device to be practical. Finally, the control mechanism must deliver a steady output flow over a range of desired pressures, and must not cut off completely delivery at high pressures.
Prior art elastomeric flow controls have had to be encased in a surrounding casing to strengthen them in the region near the flow passage orifice, or their response to pressure input was to cut off at extremely low pressures so that no flow would result. In most applications, flow cutoff is a result that cannot be tolerated in any event.
Since the construction of the prior art constant flow elastomeric restrictors to avoid early flow cut-off required encasement of the elastomeric restrictor, manufacturing costs are relatively high and quality control problems are compounded. Without encasement, the restrictor shuts off all fluid flow at a relatively low pressure in prior art designs. Hence, until now, it has been impossible to make a single, integrally molded device from an elastomeric compound which will have adequate response to a wide range of pressures.
Thus, the prior art elastomeric restrictors have suffered, to varying degrees, from insufficient constant flow response to varying pressures and high unit costs in manufacturing. Accordingly, the present invention minimizes these critical problems in this art.